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If Google is changing the rules, it doesn't really matter if you make changes or not, in some cases. For example, we've seen issues recently where Google tweaked domain diversity and gave more spots to the same domains. In some cases, that pushed other people down, even though those other people didn't do anything wrong. In many cases, Google seems to test changes and then adjust, so you can see ups and downs. In other cases, I've seen situations where Google pumped up "freshness" (QDF), either overall or for certain queries. So, sites with new or updated content suddenly got a boost, and sites with older content got pushed down, even if those sites didn't do anything. Of course, it's also always possible that your competition has made changes. Even if you change nothing, other people are constantly changing their sites. Now, if only you are bouncing around, and the rankings are otherwise pretty consistent, then it is possibly a sign of a problem. You could be facing a potential penalty, for example, or some of your links or content are being devalued. This can range from something simple and no fault of your own (a site that used to link to use no longer does) to a full-scale penalty brewing. It can be really tough to diagnose "bounce", but it's much more common than I suspect most people think it is.

Good luck to you! I plan on opening an SEO/ Internet Marketing company in about 2 years. I don't plan on going global either but it is a nice business to be in.